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Soil and Groundwater Investigation Report ARCO Facility No 6100 Tracy, California • Page 3 • Completed the soil boring as a 4-inch diameter groundwater monitoring well Prior to implementation of field activities, a well construction permit was obtained from San Joaquin County PHS/EHD An encroachment permit to close one lane of Patterson Pass Road during drilling was obtained from San Joaquin County Public Works Department Underground Service Alert (USA) was notified 48 hours prior to work activities, and a subsurface utility locator cleared the drilling site San Joaquin County PHS/EHD and CRWQCB were subsequently notified of the work schedule and representatives from both agencies were on site at various times throughout the drilling activities All work was performed under the direction of a California Registered Geologist Soil Boring and Sampling A Delta Staff Geologist was onsite to oversee Water Development Corporation Inc (WDC) of Woodland, California conduct the drilling and well installation activities The location of the soil boring is shown on Figure 2 Depth to water measurements were collected from the vapor extraction wells located in the vicinity of the boring prior to drilling Water was not present in any of the wells with the exception of VW-20, which contained less than a foot of water in the casing (threaded bottom cap is approximately 0 5 feet) The initial five feet of the boring was advanced with a hand auger to reduce the possibility of damaging underground utilities Drilling was conducted using an air-rotary casing hammer drill rig The boring was advanced from 0-100 feet bgs using a tri-cone drill bit Soil samples were obtained by withdrawing the drill stem and replacing the drill bit with a split-spoon sampler A 5-cone open-throated drill bit was used from 100 to the total depth of the boring This equipment enabled the collection of samples directly through the drill bit Steel 10-inch diameter drive casing was advanced during drilling to prevent the borehole from collapsing At approximately 90 feet bgs, advancement of the drive casing became extremely difficult At 117 feet bgs, the drill rig was unable to further advance the casing Following a mechanical breakdown on August 25, 2000, the drive casing was withdrawn from 117 to 100 feet bgs Drilling resumed the following day without further advancement of the drive casing The boring was completed to 202 feet bgs on August 28, 2000 To increase drilling efficiency, a small amount of water was added through the drill stem while drilling, beginning at approximately 90 bgs The addition of water was discontinued at approximately 2 feet above each designated sampling point After the drilling operations were completed, it was noted that water was entering the • borehole at a very slow rate (initially less than 3 feet per hour) The boring was undisturbed for approximately 20 hours at which time the incoming water had stabilized